A person’s intake of refined sugar and of foods that break down into sugars during digestion is the dietary source of virtually all of the glucose (a type of sugar) that reaches that person’s bloodstream. Coffee, however, which itself does not break down into sugars during digestion, sometimes causes a person’s blood-glucose level to rise dramatically, even if the coffee is consumed without cream or anysweeteners.

Which of the following, if true, best helps to explain coffee’s effect on blood-glucose levels as it is described above?

People often drink coffee after a meal consisting of several types of foods that themselves rapidly break down into sugars during digestion.

Drinking more than two cups of coffee in an hour increases a person’s level of stress, and the body reacts to stress by releasing stored glucose into the blood.

People who eat very few foods that contain refined sugar often have higher blood-glucose levels than people who eat many such foods.

For many people, the consumption of one piece of chocolate cake has the same stimulating effect as one cup of plain coffee.

People with sedentary office jobs are more likely to drink large amounts of coffee and to have higher blood-glucose levels than are people with jobs requiring constant physical activity.

The use of nets at beach resorts to protect swimming areas from sharks has been criticized by environmentalists because the nets needlessly kill thousands of marine animals annually. However, environmentalists have recently discovered that an electrified cable buried beneath the periphery of swimming areas causes sharks to swim away while harming neither humans nor marine life. Hence, by installing such cables, resort communities will be able to maintain tourism while satisfying environmentalists’ concerns.

Which of the following, if true, most seriously weakens the argument?

Many seaside resort communities where sharks have never been sighted nonetheless plan to install the new technology.

Tourism at resorts where sharks have been sighted has suffered only slightly despite the fact that most people claim to fear sharks.

Most tourists are unlikely to visit beaches where swimmers cannot actually see the barrier that protects them from sharks.

The buried cable is not the only innovation approved by environmentalists that is known to be successful in repelling sharks without harming them.

The electrical current produced by the buried cable repels many kinds of fish but not the marine mammals that are a tourist attraction at many resorts.